Improvements in battery design and electric drive system technology have led to a significant increase in the number of applications for electric vehicles and also the quantity of electric vehicles in use in the world today. For example, in industrial settings, electric vehicles including electrically powered forklift trucks and electrically powered mining vehicles such as shuttle cars are prevalent. In recreational settings, electrically powered golf carts have essentially become the standard for this industry.
It is anticipated that future technological advances will act in conjunction with the needs to conserve energy resources and reduce pollution and lead to the development of electrically powered vehicles for use as commuter transportation.
Virtually all of the electrically powered vehicles of the type described rely upon energy stored in batteries to power their operation. With the exception of certain solar powered vehicles, the batteries are connected by flexible electrical cables and cooperating electrical connectors to charging systems when the vehicles are not in use. These charging systems are designed to bring the batteries to "full charge" so that all possible energy is available to the operator when the vehicles are returned to operation.
In most prior art electric vehicle charging systems, it is possible to drive the vehicle while still connected to the battery charger. This unfortunately represents a significant hazard as the vehicle connector for the battery charger may be jerked from the vehicle charger receptacle and the charger receptacle, connector and/or cables may be damaged. It is also possible for the battery charger unit to be jerked from its place of rest and damaged, for example, as a result of a fall from a shelf. Of course, physical injury could also result from such an incident taking place.
From a safety standpoint, it is therefore quite desirable to have a vehicle battery charging system that prevents the vehicle from being operated while connected to the charging system. This desire has been recognized and was previously addressed in the art as is made evident from a review of U.S. Pat. No. 3,898,547 to Poole. The Poole patent relates to an electric vehicle battery charger interlock system that prevents the vehicle from being driven while the batteries are being charged. More particularly, when the plug at the end of the charger cables is engaged in the charger receptacle on the vehicle, a series circuit is completed through a relay that energizes a coil. The relay disconnects the vehicle speed control solenoid circuit from the battery therefore making the vehicle inoperative.
While the interlock system disclosed in the Poole patent does operate to prevent operation of the drive motor during the charging operation, it must be appreciated that the system is relatively complex and cumbersome. It is both expensive to produce and maintain. The dependability of relay systems in the operating environment of these vehicles is also always a concern.
Recognizing these and other shortcomings a new charger receptacle was subsequently developed for an electric vehicle. This receptacle, as presently incorporated on many Yamaha golf carts, utilizes a microswitch that operates to interrupt the circuit to the drive motor when the charging system is connected to the vehicle. The microswitch is activated by means of an outwardly projecting push button situated between the female contacts of the charger receptacle. More particularly, when fully inserted into the receptacle, the face of the charger plug engages the push button actuator thereby interrupting the circuit between the battery and drive motor of the vehicle.
While substantially reducing the cost of production and maintenance over the Poole interlock system design, this system also suffers from various shortcomings. The main shortcoming has to do with the failure of the system to ensure interruption of the circuit to the vehicle drive motor when connection is made with the battery charger.
More particularly, it is possible for the male contacts of the charger plug to be inserted sufficiently into the female contacts of the charger receptacle to provide connection for charging without the charger plug being sufficiently inserted into the receptacle to engage the actuator button and trip the microswitch. In fact, such a condition usually persists with this arrangement as it is often difficult to insert the charger plug fully into the charger receptacle. This is particularly true after the system has been used for some time as the prong contacts of the charger plug tend to become bent and damaged even when ordinary care is exercised.
When this fact is considered in light of the quick pace in which individuals are usually making this connection, it is clear that this system often fails to provide its desired function. As a result, in the haste to place an electric vehicle in operation, vehicles incorporating this system are often operated with the charger plug connected. This results in the charger plug being jerked from the charger receptacle on the vehicle. Consequently, the plug or cables and even the receptacle may be damaged, requiring down time for maintenance. Additionally, an operator may be injured by the snapping motion of the plug or cables as the plug pops free of the receptacle.
It should therefore be appreciated that a need exists for an improved electrical connection apparatus between an electric vehicle and battery charger.